The invention relates to a method for operating a laser light source, in particular for scanning in a confocal scanning laser microscope, the laser light source being supplied with electricity via a power pack. The invention also relates to a method for operating a pulsed laser light source.
In a confocal scanning laser microscope, or in the laser scanner therein, the laser light source is the most expensive component, with a price in the region of between DM 10,000 and DM 20,000, the life of the laser light source being a few thousand hours. The prior art has already disclosed a measure for extending the life of the laser. Specifically, it is already known to produce a so-called standby circuit, through the activation of which the laser is set to a minimum power status in which the gas discharge of the laser is just not quite struck. If the laser is not being used, and if the standby is therefore activated, procedures for switching on and off are not needed. The tube current is returned to the requisite operating level shortly before use, for example after a period during which no processing has been carried out.
When a confocal microscope is being used conventionally, the effective working beam time, i.e. the effective acquisition time, during which the laser light is actually used at full power, is extremely short. The majority of the overall operating time of a system of this type (usually more than 90%) is needed for preparing the experiment and for evaluating the data, while the laser light source generally remains switched on. This means that, for most of the time that it is switched on, the laser light source is not being used for anything, and therefore is being operated in a way that shortens its life.
It is also known that, in the case of gas lasers, for example argon or krypton lasers, their life decreases exponentially as the tube current increases.
The object of the present invention is therefore to extend the life of the laser light source through optimized operation, thereby reducing the overall operating costs.
The process according to the invention, of the generic type, achieves the above object through the features described herein. Accordingly, in a process for operating a laser light source, the laser light source is operated with the requisite power essentially only during the working beam time, preferably during the data acquisition. In the case when a pulsed laser light source is being used, the working beam time, in particular the data acquisition, is essentially synchronized with the emission cycle of the laser light source.
According to the invention, it has been established that, in particular in the case of confocal scanning laser microscopes, the laser light source is not being used for anything for most of the time that it is operated. This is due not only to genuine interruptions to work, in the course of which a conventional standby mode can be selected, but further to this laser light sources are only partially used during the data acquisition, even during the line cycle (e.g. in the x direction) or during the frame cycle (for example in the y direction). It may thus be assumed that, during the line cycle (in the x direction), only 25% of the time requirement of the overall cycle is needed for the x-scan in one direction. Because the inertia of the mirror is not negligible, it can be estimated that a further 25% of the total time is taken up by the respective changes in direction of the scanner. The same is true for the return travel of the scanner on the x axis, and for the further turn around for new run or scan.
If, in the scope of such a line cycle, detection were to be carried out only in one direction along the x axis, the laser light source would be used for only 25% of its total operating time. It can also be assumed that the frame cycle for the return travel to the starting position of the laser beam takes a further considerable amount of time, and this can also be estimated at about 25% of the total time. Consequently, the actual working beam time relative to the line cycle and the superimposed frame cycle would be 25% (or 50% for an operating procedure in both directions along the x axis) of 75% (the usable time in the y direction).
On the basis of the above considerations, it has been established according to the invention that the tube current of the laser ought to be reduced, and above all can be reduced, whenever this is possible taking into account the actual working beam time. In the optimum case, the laser is (fully) powered exclusively during the time for which the data acquisition takes place in the case of use in a confocal scanning laser microscope. In other words, the laser is switched at least to a substantially lower power during the return-travel times for the scanner in the x-y-z directions. In any case, the laser light source is operated with the requisite power essentially only during the working beam time, preferably during the data acquisition.
However, conventional types of lasers are complicated, and therefore expensive, insofar as if they are produced in large sizes they require a great deal of cooling. This is not the case with so-called xe2x80x9cdeep UV lasersxe2x80x9d, such lasers being available with sufficient power using the wavelengths 224, 248, 260, 270 or 280 nm in the form of vapor/gas lasers (HeAg, NeCu, HeAu). These lasers are, however, pulsed, which is a disadvantage for confocal scanning laser microscopy, and this being the case they usually have a duty cycle of from 50% down to only a few percent, for example 5%. The pulse repetition rate is also very low, so that to date these lasers have not been suitable as light sources for a scanning laser microscope.
As an alternative to the process described above, it is now also possible (in the scope of independent patent claim 2), to use such deep UV lasers in confocal scanning laser microscopy, in that to be precise the working beam time, in particular the data acquisition, is essentially synchronized with the emission cycle of the laser light source. In other words, the duty cycle of the scanner is matched to the duty cycle of the laser light source.
The following numerical example demonstrates the relevance of such an application:
With the PRF (pulse repetition frequency) of 500 Hz (=2 ms) and a duty cycle of 5% (=0.1 ms), a match to a scanner for the x direction with a line frequency of 8 kHz (=125 xcexcs period) could be made as follows: one of the two xe2x80x9clinearxe2x80x9d ranges usable for scanning is equal to one quarter of the period, i.e. approximately 30 xcexcs. Within the 0.1 ms (100 xcexcs) duty cycle of the laser, it is therefore possible to scan about 2 lines. However, a prerequisite for this is that, shortly after the start of the light pulse, the scanner is at the start of a xe2x80x9clinearxe2x80x9d scan region and can scan the first line. If the scanner also scans in the y direction during this duty cycle, a further line is also scanned during the return travel in the x direction, since the laser light is still xe2x80x9cturned onxe2x80x9d. An x scanner with a low frequency (for example 4 kHz) can then, with suitable synchronization, only record one line per duty cycle. This may, however, in the case of weak fluorescence signals, be advantageous for the measured signal-to-noise ratio.
The scanning therefore takes place only during the duty cycle of the laser, and the acquisition process is idle for the rest of the time.
Notwithstanding the alternative embodiments of the process according to the invention which have been explained above, the laser power can in principle be reduced outside the working beam time, i.e. whenever the full laser power is not needed. Such a reduction in the laser power outside the working beam time, i.e. application of reduced power to the laser light source, can be achieved by conventional dimming of the laser light source, so long as the type of laser is suitable for this. As a concrete example, the power of the laser light source could be reduced to about 20%, and in the scope of a particularly advantageous embodiment, the laser power is reduced outside the working beam time such that the laser light source is just still on.
It is also conceivable for the laser to be supplied with electricity only during the working beam time, or put another way it is at least briefly turned off outside the working beam time. In order to turn the laser light source on again, a special starting aid could be employed, with the specific intent of reobtaining a usable laser beam as quickly as possible.
In order to achieve the measure according to the invention, it is possible that the laser power pack is controlled using a synchronization signal made available by the scanner. Through this synchronization signal, the laser emission is (by fast synchronization) optimally matched to the duty cycle of the scanner, so that the laser light source is only fully powered, or only operates at the full power level, if data acquisition is is being carried out in the scope of the xe2x80x9cgenuinexe2x80x9d working beam time.
It is also conceivable to configure the process described above in order to switch, or modulate, a laser light source in such a way that lasers of the same power are driven in modulated operation with higher power, but without thermally overloading them. Ultimately, this gives rise to power spikes which just still permit this kind of modulated operation. In this case, it is even possible, with a small air-cooled laser, to increase the power over an albeit relatively short data acquisition time for a line up to a level where even UV lines start to lase. The demand on the laser cooling system is in this case substantially less in comparison with continuous operation at the maximum power level.
If the laser light source is being used for scanning in a confocal scanning laser microscope, the full-power working beam time could be defined by the data acquisition during preferably meandering line cycles. The sample would then be scanned in a meandering way. In this case, especially when a pulsed laser light source is being used, it is possible to make the data acquisition take place in every n-th line, preferably in every second line, with the specific intent of being able to exploit the duty cycle of the laser light source fully. Scanning would then be carried out exclusively during the duty cycle of the laser, irrespective of how many lines are covered outside the duty cycle of the laser light source.
Lastly, it is also conceivable to carry out the return travel of the scanner through preferably meandering line cycles, with the specific intent of effectively minimizing the actual return-travel time in the scope of the frame cycle. The same procedures as in the aforementioned line cycle in the x direction then apply.
There are now a variety of possible ways of refining and developing teaching of the present invention in an advantageous fashion. In this regard, reference may be made on the one hand to the claims subordinate to independent patent claims 1 and 2, and on the other hand to the following explanation of the process according to the invention in conjunction with the drawing. In connection with the explanation of the process according to the invention, advantageous embodiments will also be explained. In the drawing.